The present invention relates to a solid insulator-type vacuum switch gear having a pair of terminals and an insulator housing which is covered by an outer grounded cover and which in its inside comprises a vacuum switching chamber and, wherein between the switching chamber and the insulator housing gas is provided. Such vacuum switch gear having solid insulator housing are preferred for the ready-made type high voltage switching apparatus or transformer stations, wherein the requirements with respect to touch contact and with respect to space savings and compact structure are very high.
It is known to provide within the switch gear a vacuum switching chamber which comprises an evacuated housing therein along with metallic shields.
A fixed contact member is arranged on a fixed contact rod which is led out from the housing in a vacuum tight fashion through an insulator. A movable contact member is on the other hand arranged on a axially movable contact rod which is led out in a vacuum tight fashion from the housing through an insulator and metal bellows. Furthermore, there are provided metallic shields lying at a free potential between the insulators. Between the vacuum switching chamber and the insulator housing there is either air (German Pat. No. 23 22 372), or the intermediate chamber is filled with an insulating oil (Japanese Pat. No. 55-5651).
In the event in the intermediate chamber between the switching chamber and the insulator housing air is provided, then in spite of the field controlling structure of the coupling members on the electrically highly stressed paths, partial electrical discharge may take place, which is unavoidable.
Switch gear having oil in the intermediate chamber, possesses similar disadvantages as the so-called oil-less switch gear, since they are susceptible to fire hazard and represent also an endangerment for the environment. Furthermore, it became known to embed the entire vacuum switch chamber in epoxy resin (German Laid-Open Appln. No. 22 40 106). This construction, however, gives rise to disadvantages due to the fact that inner mechanical tensions effecting the vacuum switching chamber are unavoidable, and cracks as well as air gaps and air pockets may form which cannot be reliably prevented. In such defects then electrical partial discharges may take place which have the well known destructive consequences.
The above-described solid material and air insulated vacuum switch gear have in addition the further disadvantage that they cannot be touched while they are in operation and in order to satisfy the touch protection requirements, they must be built into metal encapsulated units, or provided with addtional enclosures. These disadvantages can be eliminated in a known manner, by the simultaneous reduction of the dimensions and applying the principle of solid material insulation acccording to which the entire current path and all components under high voltage are embedded in solid insulating material on the upper surface of which a grounded metallic shield is provided (Journal Elektrie 28 (1974) Volume 10, pages 533-538).